Single ended sensing is often used with a matchline (ML) in Content Addressable Memory (CAM) and a bitline in eight-transistor Static Random-Access Memory (8T SRAM). Sensing is performed in two non-overlapping phases (PRE-CHARGE and SENSE) each controlled by GLOBAL sensing signals. That is, matchlines or bitlines are pre-charged and then evaluated (e.g., sensed). In SRAM cells, each phase, e.g., pre-charge and sensing, has been timed to bound both 5 sigma weak PRE-CHARGE entries and 5 sigma weak SENSE entries, satisfying a very low-probability of having a single entry be both 5 sigma weak for PRE-CHARGE and 5 sigma weak for SENSE entry.
As technology scales to submicron geometries, random device variation (RDV) is becoming more prominent, with its effects especially evident in the design of semiconductor memories. That is, RDV is becoming a major bottleneck for improving performance. For example, as device variation increases, timing uncertainty for signal arrival and data capture increases, requiring larger data capture margins, and therefore limiting performance. RDV of parameters can include transistor length, transistor width and transistor threshold voltage even in identically designed neighboring devices.
By way of illustration, conventional self-referenced sense amplifiers require a globally timed signal, i.e., a clock-based signal that is applied to plural sense amplifiers, to stop the pre-charge phase and begin the evaluation phase. Using a globally timed signal causes a plurality of sense amplifiers to have the same amount of pre-charge time. However, due to process variations, some sense amplifiers may not require the full pre-charge time in order to reach their particular pre-charge level. This results in some sense amplifiers sitting idle in the pre-charge phase after they have reached their pre-charge level but before the globally timed signal turns off the pre-charge. Accordingly, large over-bounding for timing uncertainty can be caused by RDV-induced timing uncertainty, with globally timed sensing signals.